Intermittent electrical faults are physical events that manifest themselves occasionally and in often unpredictable ways within electrical systems or networks. When an intermittent fault occurs in a system, the system may produce erroneous results or could fail. To take some specific examples of particular electrical faults that occur in networks, a wire may rub against a neighboring wire and a small electrical arc may be created as a result of the contact. In another example, a clamp may break through the insulation surrounding the wire and touch the wire creating a fault. In yet another example, a wire may break at the back end of a connector thereby creating a fault. In still another example, corrosion may create intermittent non-contact between wires and pins within a given system. In another example, cracks on wires within the system may have water dripping on them (or the wires may be in contact with other substances) thereby creating electrical faults. Internal coil turn-to-turn insulation in electric machines may also fail in systems with electrical coils creating electrical faults.
The consequences of intermittent electrical faults can be severe and, in many instances, can cause substantial damage to the electrical equipment, can result in injury to users, or can even cause the loss of human life. For instance electrical fires may be sparked because of the occurrence of some electrical faults. When the faults occur in aircraft, fuel tank explosions may occur if electrical faults occur near a fuel tank. Even if catastrophic damage or injury does not occur, the operational lifetime of machines or systems may be reduced as the result of the occurrence of intermittent electrical faults. One characteristic of intermittent faults is that they are random and unpredictable. Their recurrence is also unpredictable. However, if an intermittent fault is left undetected and un-repaired, a major, disastrous, and permanent fault might follow that may cause deaths, failures, or destruction.
Previous attempts at identifying electrical faults have relied upon the visual or instrument-aided inspection of electrical systems. However, various disadvantages exist with these previous approaches. For example, the operation of the system frequently had to be suspended to determine if a fault existed thereby causing various problems such as loss of revenue for the owner or operator of the system. Moreover, many locations within existing systems were frequently hard to reach and/or observe thereby severely limiting the effectiveness of these approaches. These previous approaches also proved unable to detect the fault in many cases since the duration of the fault was often short and the system would behave normally as if nothing happened after this short-lived intermittent fault event. Therefore, it was relatively easy for the observer to miss the occurrence of the fault. Additionally, these approaches often relied upon intrusive placement of any equipment used frequently leading to at least some disruption of the existing system.
Other previous approaches relied upon transmitting electromagnetic waves across the network being observed. In one previous example, pulses were transmitted in networks and any reflections were analyzed to determine if a fault existed. More specifically, incident standing waves or impulses were transmitted and then reflected in the network, and then the time between the incident pulse and the reflected pulse was calculated to determine the distance to the location where the pulse was reflected. Different criteria were then used to determine if the reflection was a potential fault. One problem with this technique was that any change in the wire material (e.g., a branch-out in the network) reflected the incident waves resulting in erroneous fault determination. Another problem with this technique was that it required the transmission of high voltage pulses, which some electrical systems with thin coils (e.g., with short wires or thin windings) could not endure. Another time domain reflectometry method employed spread-spectrum techniques, but this approach did not solve the above-mentioned problems since high voltage pulse transmission was still required and reflection still occurred on branches of the electrical network.
Another previous approach transmitted direct-sequence spread-spectrum modulated signals, instead of high voltage signals, and employed signal processing techniques in an attempt to find and locate electrical faults. These approaches, however, still relied on reflectometry that is, sending incident signal and receiving reflected signal and the timing of them for distance calculation. As a result, although this approach may have, under some circumstances, overcome the need to use high voltage incident voltage pulses, it still had the problem of reflection occurring at all points of branching in the network and in the devices that were connected.
Still another problem of the reflectometry approach was that the location of the device must be close to one end of the electrical system, either the line end or the source end. Otherwise, the injected signal would be reflected from both ends and result in a combined, distorted, and reflected signal. This requirement of locating the device at either end is very difficult to meet since many electrical networks are connected in a complicated format, often in a mesh architecture.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.